Photographic colour material

ABSTRACT

A PROCESS FOR THE MANUFACTURE OF A PHOTOGRAPHIC COLOUR IMAGE WHICH COMPRISES EXPOSING IMAGE-WISE AND PROCESSING IN THE PRESENCE OF A DYE BLEACH CATALYST, A PHOTOGRAPHIC MATERIAL CONTAINING AT LEAST ONE SILVER HALIDE EMULSION LAYER CONTAINING A DIFFUSION-RESISTANT BLEACHABLE   IMAGE DYESTUFF AND IMMEDIATELY ABOVE AND BELOW SAID LAYER, TWO SILVER HALIDE EMULSION LAYERS, FREE OF IMAGE DYESTUFF, AS WELL AS A PHOTOGRAPHIC MATERIAL CONTAINING SAID LAYERS ARE DISCLOSED.

July 3, 1973 'c. BORAGINE ET AL 3,743,506

PHOTOGRAPHIC COLOUR MATERIAL Filed July 7, 1971 United States Patent ()ffice 3,743,506 Patented July 3, 1973 3,743,506 PHOTOGRAPHIC COLOUR MATERIAL Carlo Boragine, Route de la petite Fin 6, and Armin Meyer, Chemin du petit Rhone 36, both of Fribourg, Switzerland Filed July 7, 1971, Ser. No. 160,561 Claims priority, application Switzerland, July 7, 1970, 10,266/70 Int. Cl. G03c 1/76 US. Cl. 96-73 21 Claims ABSTRACT OF THE DISCLOSURE A process for the manufacture of a photographic colour image which comprises exposing image-wise and processing in the presence of a dye bleach catalyst, a photographic material containing at least one silver halide emulsion layer containing a diffusion-resistant bleachable image dyestuff and immediately above and below said layer, two silver halide emulsion layers, free of image dyestuff, as well as a photographic material containing said layers are disclosed.

A customary material for the silver dye bleach process contains, on a transparent or reflecting support, an emulsion layer, dyed with a blue-green dyestuif, which is sensitive to red, on top of this an emulsion layer, dyed with a purple dyestuff, which is sensitive to green, and uppermost an emulsion layer, dyed with a yellow dyestuff, which is sensitive to blue. Additionally, filter layers and other intermediate layers can be present between these emulsion layers. Other layer sequences and other sensitiser arrangements are also possible. Such a material is exposed, developed and finally processed to give a coloured image by bleaching the image dyestuffs present as a function of the developed metallic silver, and removing the excess silver halide and metallic silver from the material.

The known materials, and the processes effected with them, display various disadvantages which it has hitherto not been possible to overcome completely.

If only as much silver halide is employed in the photographic material as is required for bleaching the dyestuff, a material of completely inadequate light sensitivity is obtained. In general, therefore, a large excess of silver halide is used, a large excess of silver is produced, and only part of the developed silver is used for bleaching the dyestuff. In this way, a higher, but still inadequate, light sensitivity is achieved. This is due to the fact that the silver halide emulsion is frequently chemically desensitised by azo dyestuffs, and that the dyestuffs also cause optical desensitisation, that is to say absorb light in the spectral sensitivity range of the emulsion, so that the light is reduced in intensity in the layer, and no longer exerts an effect in the depth of the layer.

Even if, for special purposes, the sensitisation range lies outside the absorption range of the dyestuif, there is always a chemical desensitisation by the dyestutf.

According to British patent specification 421,727, these disadvantages are overcome by not dyeing the lightsensitive layer, but separating the layer into an upper (that is to say facing the light source) colourless emulsion layer and a lower layer, dyed with image dyestuif, which is not sensitive to light. If such a layer is developed, a. silver image is obtained in the upper layer, and under the influence of this image the dyestuff of the lower layer can be bleached according to British patent specification 514,955. This remote bleaching is possible through the dye bleach catalyst (for example 2,3-diaminophenazine) being activated on the silver, the activated form migrating to the dyestuff and there bleaching the dyestuif. To carry out this process, a very large amount of silver, long bleaching times and vigorous bleaching conditions are required, and these lead to undesired colour gradations.

Furthermore, the gradation of the images produced by the silver dye bleach process is as a rule too steep, especially if, in the manner which has been indicated, an excess of silver which is only partially used for dye bleaching is employed. This disadvantage was also recognised at an early stage and is, for example, counteracted according to German patent specification 733,728 by bleaching in the presence of an oxidising agent. This results in a certain flattening of the colour image, but this flattening preferentially occurs as a result of lengthening the bottom part of the colour gradation curve, that is to say at the expense'of the sensitivity; furthermore, instead of obtaining a desirable straight-line (linearised) gradation, a colour gradation curve which is greatly deformed into an S-shape is obtained through lengthening the bottom part.

Another process for flattening the gradation is proposed in US. patent specification 2,321,195 or 3,505,068. According to this, the layer is divided into two layers: a dyed layer having a sensitive emulsion and another dyed layer with a less sensitive emulsion. According to this process, again, the gradation is corrected at the expense of the sensitivity.

Other disadvantages result from effects on the adjacent layer, which can frequently only be controlled with difficulty. Thus, as long as no sufficiently diffusion-resistant dyestuffs were available, it was diflicult to prevent distortions of colours through dyestuff diffusion. US. patent specification 2,391,198 proposes a material which contains a separating layer, containing emulsion, between the emulsion layers dyed with dyestuffs which are not diffusion-resistant. According to this patent specification the silver developed image-wise in the intermediate layer serves to bleach the dyestulf which diffuses from the adjacent coloured layers. Without an intermediate layer, the dyestulf which diffuses into the adjacent coloured layer results in colour distortions. In an intermediate layer without emulsion, the dyestulf remains as a residual dye fog even when exposed to the point of whiteness.

Since, according to this patent specification, the process is carried out in the absence of dye bleach catalysts, a significant interaction affecting the bleaching of the nondiffusing dyestuff is impossible.

Processes are also known (U.S. patent specification 2,183,394 and British patent specification 483,464) which start from coloured emulsion layers and colourless emulsion layers, which serve to record various colour impressions. In these processes the colourless layers, after blackand-white development, are dyed with image dyestuffs, which then help to serve in the production of the image.

Other proposals for increasing the sensitivity are based on avoiding optical desensitisation by choosing sensitisation ranges which lie outside the absorption range of the dyestuff, or by converting colourless derivatives of a dyestulf or colourless precursor compounds of a dyestuif into image dyestuffs only after exposure.

The abovementioned disadvantages can be avoided, for example, if an emulsion layer free of image dyestuff is provided above an emulsion layer containing a diffusionresistant image dyestulf, silver-images are developed in both layers, and the image dyestufi is bleached in the presence of a bleaching catalyst so that, in addition to bleaching by the silver present in the layer, additional bleaching by the silver of the adjacent upper layer it occus. As a result of the co-operation of close bleaching and remote bleaching, an effect is achieved which advantageously influences the gradation, sensitivity and spectral distribution of the sensitivity.

A further possibility is also, for example, to provide an additional emulsion layer, free of image dyestuff, underneath an emulsion layer containing a diffusion-resistant image dyestuif, to develop silver-images in both layers and to bleach the image dyestutf in the presence of a bleaching catalyst so that, in addition to bleaching by the silver present in the layer, an additional bleaching by the silver of the adjacent layer below it occurs. Here again effects are achieved which influence the image properties in other ways.

It has now been found that a combination of the two abovementioned arrangements leads to surprising results.

The subject of the present invention is, accordingly, a process for the production of a photographic colour image by the silver dye bleach process, characterised in that a photographic material which contains, on a support, at least one silver halide emulsion layer containing a diffusion-resistant bleachable image dyestuff, and additionally on both sides, immediately above and below this layer, two silver halide emulsion layers free of image dyestuif which are of at least equally high sensitivity as the layer containing dyestutf, is exposed image-wise and is processed in the presence of a dye bleach catalyst to give a coloured image, the coloured image being produced exclusively by image dyestuffs present in the photographic material before exposure.

A further subject of the present invention is a photographic material which contains, on a support, at least one silver halide emulsion layer containing a diffusionresistant image dyestuff which is bleachable by the silver dye bleach process, between a silver halide emulsion layer above it, which is free of image dyestuff, and a silver halide emulsion layer below it, which is also free of image dyestuff, the two emulsion layers free of image dyestuff being of at least equally high sensitivity as the dyestuifcontaining layer, and preferably, all three layers being sensitive to the same spectral region.

The colourless emulsion layers are above and below the dyed emulsion layer. The result of this is that the sensitivity of the colourless layers does not suffer the chemical desensitisation by the image dyestuif. As already mentioned, the sensitivities of the three layers must be so matched that the sensitivities of the colourless layers are as high, or preferably higher, than those of the dyed layer. An equally high sensitivity is achieved in a simple fashion by dividing a single base emulsion into three parts, adding image dyestufi to one part and casting the three parts over the top of one another. It is however also possible to start from different emulsions (different gradation and different sensitivity) for the three layers.

In order to achieve the desired effects it sufiices, in most cases, if, in the colourless layers, the amount of silver halide cast per unit surface area is adjusted to be as high, or only a fraction of, that of the coloured layer, for example to 100% Amounts of silver halide higher than 100% can also be used. The sensitivities of the colourless emulsion layers are so adjusted that the colour gradation curve is linearised through correction of the shoulder part and of the bottom part, that is to say approaches a straight line. This must be determined empirically. The shoulder sensitivity of the coloured layer is increased by remote-bleaching by the upper layer, which is free of image dyestufi. As a result of remote bleaching by the lower layer which is free of image dyestuif, an increase in the bottom sensitivity of the coloured layer is achieved.

Maximum gain in sensitivity together with good linearisation of the colour gradation is achieved if the colourless emulsion layer on top is rendered so extremely sensitive that if this layer were present as the sole additional layer, it would assist the bleaching of the dyestuff whilst disturbing the linearity above the shoulder region, and would thereby lead to a shade separation, and if the sensitivity of the lower colourless emulsion layer were then so adjusted that under its influence the middle part of the colour gradation curve is again linearised,

frequently doubted possibility of a silver dye bleach exposure material can finally be realised.

The optical sensitisation of the three layers which belong together preferably lies in the same spectral range. It is however not necessary to use the same optical sensitiser for the three layers. Thus, for example, the maximum of the sensitisations can be displaced by a few nm., or the maxima of the sensitisation ranges can differ from one another. Additional sensitivities in other spectral ranges can be desirable for producing certain masking effects. If the three layers are sensitised in each range in which the image dyestuif also absorbs, it is advisable to choose an emulsion of extremely high sensitivity for the lower, undyed, layer, and/or to sensitise this layer towards shorter wavelengths of preferably towards longer wavelengths (relative to the absorption maximum of the image dyestuff).

Where this description speaks of colourless or dyestufffree emulsion layers, this is to be understood as meaning that this emulsion layer is free of image dyestuff. This description is however not intended to exclude the possibility that it may contain a filter dyestutf, as a result of the presence of which the spectral transmission during exposure is selectively reduced and/or the image sharpness increased. Such a filter dyestulf is completely destroyed or eluted during processing in baths.

The process according to the invention is suitable for monochromatic and polychromatic material. It is of particular importance in producing polychromatic images, because the requirement that the gradations and sensitivities of the individual coloured layers should be matched to one another reduces the number of possible variations.

A polychromatic material according to the invention contains at least two silver halide emulsion layers containing image dyestuffs, the two image dyestuffs being different from one another, and can, according to the invention, contain one or more three-layer systems. These three-layer systems can, if desired, be separated from other emulsion layers by intermediate layers, and these intermediate layers can also contain customary additives, such as filter dyestuffs, UV-absorbers or oxidising agents.

In the multi-layer systems, each dyed emulsion layer possesses a colourless emulsion layer immediately above it and a colourless emulsion layer immediately below it, so that the dyed emulsion layers are separated from one another by two colourless intermediate layers and optionally by an intermediate layer lying between them.

Suitable pyrazines, quinoxalines or phenazines are preferably used as dye bleach catalysts. The catalysts can be present either in a photographic processing bath or in any desired layer of the photographic material which is to be processed.

The image dyestuffs are, as a rule, azo dyestuffs.

The process according to the invention is particularly suitable for photographic transparency material having a colour density of 2.4 to 2.8, preferably 2.6.

The material according to the invention is advantageously used in building up a false colour film for infrared photography. By invoking the presentinvention, it is possible to produce an infrared exposure material of sufliciently high sensitivity. A preferred material has, for example, the following construction:

' protective layer {colourless emulsion 1ayersensitive to green yellow emulsion layersensitive to green {colourless emulsion layer-sensitive to green intermediate layer colourless emulsion layersensitive to red purple emulsion layer-sensitive to red {colourless emulsion layersensitive to red intermediate layer colourless emulsion layersensitive to infrared blue-green emulsion layer-sensitive to infrared colourless emulsion layer-sensitive to infrared transparent substrate A further application of the invention is illustrated by The following are cast onto the transparent support: the following construction: (I) layer 2, for comparison rotective layer I la la la 1' rgiilourless emul sion layeP-sensiittiive to glue in yer 1+ yer 2+ ye 3 1 5 f l 2 lle-greefl emu S1011 H ayers are cast so as to appy 1. g. o siver m.

i i 1 ,ifiglffifiif layer'qsens We to b The cast materials I and II are exposed from above {gig 1 s s gpgsigi ayeg gfinsg g fi behind a grey wedge with an infrared filter, and are proccolourless emulsion layer-sensitive to green essed as follews: intermediate layer colourless emulsion layer-sensitive to red 6 mlnutes developer pulrplelemulsioii ilayeirsensitiviatfo rgd d 10 G, CO 0111 ess emu S 011 ayersens V6 0 re transparent substrate p-Methylaminophenol sulphate ...--1 -n 2 A film having this construction possesses a normal exfi g p Sodmm sulphlte g posure sensitivity. A grey wedge is reproduced in the y g b ,4 2 correct sense by this film. A colour scale is reproduced 5 Anhy .rous so car (mate 0 1 Potassium bromide 2 with incorrect colours.

In order to reproduce the original colours, it is neces- Water to make up to 1000 sary to copy the images twice with the same material. 2 minutes stop-fixing bath A copying material of the following construction however provides the possibility of obtaining true-to-nature g gi 2? copies directly from the exposure material described Sodiim sz g 2 3) e "g" 25 above. 2

rotecme layer Glacial acetic acid 1 ml 13 colourless emulsion layer-sensitive to blue Water to make p to 1000 purple emulsion layer-sensitive to blue colourless emulsion layer-sensitive to blue 25 4 mi t s soakmg. intermediate layer or yellow filter colourless emulsion layer-sensitive to red 20 minutes dye bleach bath yellow emulsion layersensitive to red cttilourlgssterriulsion layer-sensitive to red Water ml 500 n erme 1a e ayer colourless emulsion layer-sensitive to green Sulphunc acld (96%) 14 g gg w l s ig i e r n Crystalline sodium hypophosphite g 1 ur ess emu s on ayersens we 0 reen transparent or opaque white substrate g gqj q z 3' di th 1 1 g BIIZOY aminome Y qumoxa 1116 mg The sensitivity of this material corresponds to that of a photographic positive material. Water to make up to 1000 ml.

In the three photographic materials specified it is only necessary, according to the invention, for at least one 2 mmutes soakmg' of the three coloured emulsion layers to be present as a 6 minutes silver bleach bath so-called triple layer. The protective layer and the inter- Water m1 500 mediate layers are also not absolutely essential. Sulphuric acid (9.6%) 27 EXAMPLE 1 40 Crystalline copper sulphate g 20 Potassium bromide ..g 60

A photographic material having the following layer arrangement is manufactured: Water to make up to 1000 3. Colourless emulsion layer 2 mmutes soakmg' 2. Coloured emulsion layer 4 minutes fixing bath 1. Colourless emulsion layer Substrate transparent Composition as for stop fixing bath.

The same emulsion is used for all three layers. It is 8 minutes soakmg' a silver bromide emulsion containing 1.5% of iodide, Two 9 wefiges I and H! inverse to the original 53 of Ag/kg and 70 f ge1atine/kg Thetwo colour. are obtained, which are measured behind a red filter. less emulsion layers contain, as the optical sensitizer, 3 The results of these measmements are glven the table f the compound f the f r la below. The lower the value of the relative sensitivity log (I) E, the greater is the sensitivity. v

9 e 55 CZHs- CH=CH-CH /IIC2H5 Relative C t trial L ers sensitiwtylii G d t The coloured emulsion layer contains 6.5 mg./kg. of the as m e W 0g m a m I 2 1.09 -6 compound of the Formula 1 as the optical sensitizer, and H 1+2+3 0. 62 2o 13 g./kg. of the compound of the formula as the image dyestufi. The sensitizer of the Formula 1 The gradation curves of the cast materials I and H are shows a sensitisation maximum at 760 nm. The image given in the graph in FIG. 1. Here the wedge densities of dyestufi of the Formula 2 showsan absorption maximum the exposure wedge (exposure increases from left to right) at 650 nm. are plotted on the abscissa and the density on the ordinate.

Additionally, stabilisers, wetting agents, plasticisers and The table and the graph show clearly that the cast matehardeners are added to the emulsions of all three layers, rial II has a higher-sensitivity and a flatter gradation than in the usual manner. the cast material I.

7 EXAMPLE 2 The procedure indicated in Example 1 is followed. However, the layer 2 is a coloured emulsion layer, which is sensitised with 2.3 mg./-kg. of the compound of the Formula 3:

Relative Cast material Layers sensitivity Gradation The cast material II distinctly shows a higher sensitivity and a flatter gradation than the cast material I.

EXAMPLE 3 The layer arrangement is the same as in Example 1. The same emulsion is used in all three layers. It is a silver bromide-iodide emulsion containing 4% of iodide, 53 g. of Ag./-kg. and 70 g. of gelatine/kg. The two colourless emulsion layers contain 16 mg./kg. of the compound of the Formula 4 01H CH! -0H= -cH=c EN 19 \N O 03H 1,11, oH -OIL-GOOH as the optical sensitiser.

The coloured emulsion layer contains 80 mg./ kg. of the compound (4) as the optical sensitiser and 15 g./kg. of the compound (5) as the image dyestufi:

NzN...

Hg SOsH 2 The sensitiser of the Formula 4 shows a sensitisation maximum at 640 mm. The image dyestuif of the Formula 5 shows an absorption maximum at 535 nm.

Two cast materials I and II are prepared on a transparent support, in the manner of Example 1, applying 1.5 g. of silver/m They are exposed behind a grey wedge, using a red filter, and are processed as in Example 1.

Two colour wedges I and II, converse to the original, are obtained, and these are measured behind green filters.

The results of these measurements are listed in the table below. The lower is the value of the relative sensitivity log E, the higher is the sensitivity.

Relative sensitivity Cast material Layers log E Gradation The gain in sensitivity and the flattening of the gradation of the cast material II as compared to cast material I is very distinct.

EXAMPLE 4 The procedure of Example 3 is followed. The layers are however cast on an opaque white support, applying 1.0 g. of silver/mf The two cast materials are exposed, processed and measured. The results are summarised in the table below.

Relative sensitivity, Cast material Layers log E Gradation The cast material II distinctly shows a gain in the sensitivity and a flattening of the gradation as compared to the cast material 1.

EXAMPLE 5 A material having the following construction is cast:

protective layer yellow emulsion layer-sensitive to green intermediate layer purple emulsion layer-sensitive to red intermediate layer colourless emulsion layer--sensitive to infrared blue-green emulsion layer-sensitive to infrared colourless emulsion layersensitive to infrared transparent substrate (colour density -2.6)

The three layers sensitised to infrared correspond to those of Example 2.

The intermediate layers and the protective layer are gelatine layers wherein 2 g. of gelatine are applied per m The purple emulsion layer contains 80 mg./kg. of the compound of the Formula 4 as the optical sensitiser and 15 g./kg. of the compound of the Formula 5 as the image dyestuff.

The yellow emulsion layer contains mg./ kg. of the compound of the Formula 6 as the optical sensitiser and 15.4 g./kg. of the compound of the Formula 7 as the image dyestutf.

The sensitiser of the Formula 6 shows a sensitisation maximum at 550 nm. The image dyestuif of the Formula 7 shows an absorption maximum at 416 um.

All emulsion layers are cast so as to apply 1.5 g. of silver/m Exposures using sunlight with stop 8' and V second appear correctly exposed with this coloured infrared film. As a result of the absorption of blue in the yellow layer it is possible to restrict the use of a yellow filter to special purposes only.

EXAMPLE 6 The procedure of Example 1, cast material II, is followed. 3 mg./kg. of the dye bleach catalyst of the formula 8 are additionally incorporated in the coloured emulsion layer:

The cast material is exposed and processed as in Example 1, except that the dye bleach bath does not contain a dye bleach catalyst.

The developed colour wedge is measured and gives the same results as cast material H of Example 1.

EXAMPLE 7 (A) An exposure material of the following construction is cast:

The three layers which are sensitive to red correspond to those of Example 3.

The intermediate layers and the protective layer are gelatine layers wherein 2 g. of gelatine/m. are applied.

The yellow emulsion layer contains 100 mg./ kg. of the compound of the Formula 6, indicated in Example 5, as the optical sensitizer, and 2.0.5 g./kg. of the compound of the Formula 7, indicated in Example 5, as the image dyestuff. This emulsion layer is cast so as to apply 1 g. of silver/m.

The blue-green emulsion layer, which shows the intrinsic spectral sensitivity of the emulsion, contains, as the image dyestuif, 9 g./kg. of the compound of the formula Oz 503 OCH;

having an absorption maximum at 600 nm.

This emulsion layer is cast so as to apply 1.2 g. of silver/m3.

Exposures taken with the exposure meter set to 25 10 (B) A copying material of the following construction is also cast:

protective layer purple emulsion layersensitive to blue intermediate layer yellow emulsion layersensitive to red intermediate layer colourless emulsion layersensitive to green blue-green emulsion layersensitive to green colourless emulsion layersensitive to green transparent substrate In all three layers which are sensitive to green, the same emulsion as in Example 3 is used.

The two colourless emulsion layers contain mg. /kg. of the compound of the Formula 6, indicated in Example 5, as the optical sensitizer.

The blue-green emulsion layer contains 100 mg./kg. of the compound of the Formula 6, indicated in Example 5, as the optical sensitiser, and 13 g./ kg. of the compound of the Formula 2, indicated in Example 1, as the image dyestuif.

A silver bromide-iodide emulsion containing 1.5% of iodide, 53 g. of Ag/kg. and g. of gelatine/kg, which shows a lower sensitivity than the three layers sensitive to green, is used for the yellow and the purple emulsion layers.

The yellow emulsion layer contains 80 mg./:kg. of the compound of the Formula 4, indicated in Example 3, as the optical sensitiser, and 15.4 g./kg. of the compound of the Formula 7, indicated in Example 5, as the image dyestufi.

The purple emulsion layer, which shows the intrinsic spectral sensitivity of the emulsion, contains 15 g./kg. of the compound of the Formula 5, indicated in Example 3, as the image dyestulf.

Using this second material B, the sensitivity of which corresponds to that of a photographic positive material, it is possible to obtain true-to-nature copies directly from the exposure material A described above.

The visual density of an unexposed area of this copying material corresponds to 2.6 density units.

We claim:

1. Process for the manufacture of a photographic colour image by the silver dye bleach process, characterised in that a photographic material which contains, on a support, at least one silver halide emulsion layer containing a diffusion-resistant bleachable azo dyestuif, and additionally on each side, immediately adjacent this layer, a silver halide emulsion layer, free of azo dyestulf, which are of at least equally high sensitivity as the layer containing dyestuif, is exposed image-wise and is processed, in the presence of a dye bleach catalyst, to give a coloured image, the coloured image being produced exclusively by image dyestuffs present in the photographic material before exposure.

2. Process according to claim 1, characterised in that pyrazine, quinoxaline or phenazine is used as the dye bleach catalyst.

COOH

CODE

3. Process according to claim 2, characterised in that the dye bleach catalyst is present in a photographic processsing bath.

4. Process according to claim 2, characterised in that the dye bleach catalyst is present in a layer of the photo- ASA appear, with this colour film, to be correctly exposed. graphic material which is to be processed.

5. Process according to claim 1, characterised in that the layers free of dyestulf each contain to 100% of the amount of silver halide of the layer containing dyestuff.

6. Process according to claim 1, characterised in that the layers free of dyestuff each contain more than 100% of the amount of silver halide of the layer containing dyestufi.

7.. Process according to claim 2, characterised in that the photographic material is a transparent material having a colour density of 2.4 to 2.8.

8. Process according to claim 2, characterised in that the photographic material is a false-colour material.

9. Process according to claim 8, characterised in that the material is a false colour exposure material.

10. Process according to claim 8, characterised in that eht material is a false-colour copying material.

11. Process according to claim 9, characterised in that the false-colour exposure material contains, on a transparent support, a purple silver halide emulsion layer which is sensitive to red, over this a yellow silver halide emulsion layer which is sensitive to green and over this a blue-green silver halide emulsion layer which is sensitive to blue, with at least one of these coloured layers being adjoined on both sides by a silver halide emulsion layer which is free of dyestuff.

12. Process according to claim 10, characterised in that the false-colour copying material contains, on a support, a blue-green silver halide emulsion layer which is sensitive to green, over this a yellow silver halide emulsion layer which is sensitive to red and over this a purple silver halide emulsion layer which is sensitive to blue, with at least one of these coloured layers being adjoined on both sides by a silver halide emulsion layer which is free of dyestuiT.

13. Process according to claim 2, characterised in that the photographic material is an infrared exposure material.

14. Process according to claim 13, characterised in that the infrared exposure material contains, on a transparent support, a blue-green silver halide emulsion layer which is sensitive to infrared, over this a purple silver halide emulsion layer which is sensitive to red, and over this a yellow silver halide emulsion layer which is sensitive to green, with at least one of these coloured layers being adjoined on both sides by a silver halide emulsion layer which is free of dyestutf.

15. Photographic material for the silver dye bleach process, characterised in that it contains, on a support, at least one silver halide emulsion layer containing a diifusion-resistant bleachable azo 'dyestufi, between a silver halide emulsion layer free of azo dyestuff below it and a silver halide emulsion layer, free of azo dyestuif, above it, the two layers free of azo dyestutf being at least of equally high sensitivity as the layer containing image dyestuif.

16. Photographic material according to claim 15, characterised in that it has the construction of a false colour exposure material.

17. Photographic material according to claim 15, characterised in that it has the construction of a false colour copying material.

18. Photographic material according to claim 16, characterised in that it has the construction of an infrared exposure material.

19. Photographic material according to claim 16, characterised in that it contains, on a transparent support, a purple silver halide emulsion layer which is sensitive to red, over this a yellow silver halide emulsion layer which is sensitive to green, and over this a blue-green silver halide emulsion layer which is sensitive to blue, with at least one of these coloured layers being adjoined, on both sides, by a silver halide emulsion layer which is free of dyestutf.

20. Photographic material according to claim 18, characterised in that it contains, on a support, a blue-green silver halide emulsion layer which is sensitive to green, over this a yellow silver halide emulsion layer'which is sensitive to red, and over this a purple silver halide emulsion layer which is sensitive to blue, with at least one of these coloured layers being adjoined on both sides by a silver halide emulsion layer which is free of dyestufi.

21. Photographic material according to claim 19, characterised in that it contains, on a transparent support, a blue-green silver halide emulsion layer which is sensitive to infrared, over this a purple silver halide emulsion layer which is sensitive to red, and over this a yellow silver halide emulsion layer which is sensitive to green, with at least one of these coloured layers being adjoined on both sides by a silver halide emulsion layer which is free of dyestulf.

References Cited UNITED STATES PATENTS 3,620,746 =11/19 71 Barr 96-74 3,650,739 3/1972 Marthaler 96-73 NORMAN G. TORCHIN, Primary Examiner R. L. SCHILLING, Assistant Examiner U.S. Cl. X.R. 96Z0, 74 

